Purification of hydrocyanic acid



Patented Feb. 9, 1926.

UNITED STATES PATENT OFFICE.

MARK WALKER, OF LOS ANGELEC, CALIFORNIA, ASSIGNOR TO THE PACIFIC R. dc H.

CHEMICAL CORPORATION, OF EL MONTE, CALIFORNIA, A CORPORATION OF CALIFORNIA.

PURIFICATION OF HYDROCYANIC ACID.

No Drawing. v

To all whom it may concern:

Be it known that I, MARK WALKER, a citizen of the United States, and residentof Los Angeles, in the county of Los Angeles and State of California, have invented certain new and useful Improvements for the Purification of Hydrocyamc Acid, of which the following is a specification.

This invention pertains to the purification of liquid hydrocyanie acid, particularly to products ranging from 96% to 100% purity such as is used as a commercial fumigant. The object of the invention is. to produce a product substantially free of hydrogen sulphide.

Liquid hydrocyanic acid is used in large quantities as a commercial fumigant, partieularly for the control of pests on citrus trees. The commercial product usually eontains 96 ormorepercent of hydroeyanic acid and the only other constituents besides water are small amounts of stabilizing cdmpounds such as sulphuric acid. Most ofthe hydrocyanic acid used is made from metallic cyanides that contain metallic sulphides. The chemical conditions that produce the hydrocyanic acid from the metallic salts usually liberate hydrogen sulphide as well. The hydrogen sulphide is an objectionable im urity for two important -rea sons. The rst reason is that it has a deleterious action upon equipment used for its distribution and the second reason is that as hydrogen sulphide has a tendency to cause 1 decomposition and polymerization of the liquid hydrocyanie acid when it. is in stora e.

To understand the first reason it is necessary to understand the t pes of equipment that are used for its distribution. ..These are portable pumps combined with tanks holding from one to several gallons of liquid hydrocya'nie acid. The pumps are so made that they can measure quantities of liquld 1n amounts from approximately 20 c. 0. up to 300 c. c. or more with an error of not more than or 3%. Not only must they be capable of measurement with this accuracy 60 but they must be so constructed that operators can treat a tented tree in not more than 80 seconds. This work is done at night and therefore in the darkness. The 'hvdrocyanic acid is a very volatile and ex- Application filed October 26, 1925. Serial No. 65,037.

eeptionally poisonous liquid. The pumps used for its distribution must therefore be remarkably simple in construction and so sturdily built that operating characteristics will be retained in spite of hard usage and the darkness in which they are used.

Whenever hydrogen sulphide is present inv Hydrocyanie acid is a compound that poly-- nierlzes readily with an exothermic reaction, accompanied to a slight extent at least by chemical decomposition. Polymerized hydroeyanic acid is a solid of about the physical consistency and appearance of finely ground charcoal. It-has no lubri eating properties whatever, is exceptionally insoluble in practically all chemical reagents and is exceedingly objectionable in equipment for storage and dispensing of liquid hydrocyanic acid. We have learned that hydrogen sulphide is one of the substances that tends to produce polymerization of liquid hydrocyanic acid. Its action to be sure is not as marked as that of alkaline substances such as alkaline metal carbonates, hydrogen oxides and ammonia. has much as hydrogen sulphide does have a slight tendency to accelerate polymerization, its presence in commercial hydrocyanie acid is therefore undesirable.

Hydrogen sulphide dissolves in li uid hydrocyanic acid. By the process disc osed in U. S. Patent No. 1,444,300 to Brown the hydrogen sulphide content of liquid hydroeyanic acid can be reduced to about 0.05 volume dissolved in one volume of the liquid hydrocyanie acid. On longstanding this hydrogen sulphide will gradually disappear and after several months there may indeed be no more than a trace of hydrogensulphide left. This method of elimination is too slow, however. for commercial requirements. I therefore sought means of removing the hydrogen sulphide by chemical means. The ideal rea out for the removal of hydrogen sulphi e in liquid bydrocyauic acid is one which is soluble in liquid hydrocyanic acid in all proportions; it must work rapidly; it must remove the hydrogen sulphide completely; it must not be corrosive to metals used for making drums and other appliances; it must produce no objectionable precipitate in the liquid; it must leave no dissolved solid; it mustbe convenient to use and inexpensive. I have found that for practical purposes all of these requirements are met by sulphur dioxide which is preferably introduced as a liquid.

My preferred method for removal of hydrogen sul hide from liquid hydrocyanic acid is to hrst remove all of the hydrogen sulphide possible by the process disclosed in Patent No. 1,444,300 indicated above. Thereafter I introduce a sufiicient amount of liquid sulphur dioxide or pure gaseous sulphur dioxide to completely react with the hydrogen sulphide present. I cannot state positively the mechanism of this chemical reaction but apparently some, if not all, of the sulphur is thrown out as a very fine precipitate. This precipitate is of such a nature and so small in amount that it is not objectionable. v

It is obvious that sulphur dioxide can he introduced as a water solution and I do not therefore distinguish in principle between the use of liquid sulphur dioxide, gaseous sulphur dioxide, and sulphur dioxide in solution.

What I claim is:

1. The process of purifying liquid hydrocyanicacid containing hydrogen sulphide consisting in reacting the hydrogen sulphide with sulphur dioxide.

2. The process of purifying liquid hydrocyanic acid containing hydrogen sulphide consisting in adding thereto liquid sulphur dioxide.

3. The process of purifying liquid hydrocyanic acid containing hydrogen sulphide consisting in heating the liquid within 10 C. of its boiling point, agitating the heated liquid, separating the liquid from the evolved gaseous impurities and treating the heated liquid with sufficient sulphur dioxide to completely react with the hydrogen sulphide remaining.

4:. The process of purifying liquid hydrocyanic acid containing hydrogen sulphide consisting in heating the liquid to Within 10 C. of its boiling point, separating the liquid from the evolved hydrogen sulphide and treating the separated liquid with suilicient sulphur dioxide to react with the re maining hydrogen sulphide.

5. The process ofpurifying liquid hydrocyanic acid containing hydrogen sulphide consisting in heating the liquid to "Within 10 C. of its boiling point, separating the liquid from the evolved hydro en sulphide and treating the separated liquid with sufficient liquid sulphur dioxide to react with the remaining hydrogen sulphide.

Signed at El Monte, in the count of Los Angeles and State of California his 13th day of October A. D. 1925.

MARK lVALKER. 

